docs: def _needs_format(pipcmd):
      """
      pip >= 9.0.0 needs a --format=freeze argument to avoid a DEPRECATION
      warning. This function returns True if the nominated pip executable
      is >= 9.0.0
      """
      try:
          return _needs_format_cache[pipcmd]
      except KeyError:
          pass
  
      # grab the version number
      output = run([pipcmd, '--version'], stdout=True)[1].decode('utf-8')
      m = re.match(r'^pip (\S+) from ', output)
      needs_format = StrictVersion(m.group(1)) >= '9.0.0'
      _needs_format_cache[pipcmd] = needs_format
      return needs_format